| 1. |
- Bernardo, Heliudson, et al.
(författare)
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Kalb-Ramond backgrounds in alpha'-complete cosmology
- 2021
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Ingår i: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; :9
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Tidskriftsartikel (refereegranskat)abstract
- We study the matter-coupled equations of motion for cosmological NS massless fields including all alpha' corrections in an O(d, d) duality invariant approach, with emphasis on the Kalb-Ramond two-form field B-(2) and its source. Solutions for the vacuum and matter cases are found and the corresponding Einstein frame cosmologies are discussed. We also show that the ansatz for B-(2) required by the duality invariant framework implies that the two-form is non-isotropic.
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| 2. |
- Bernardo, Heliudson, et al.
(författare)
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String cosmology backgrounds from classical string geometry
- 2021
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Ingår i: Physical Review D. - : American Physical Society (APS). - 2470-0010 .- 2470-0029. ; 103:4
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Tidskriftsartikel (refereegranskat)abstract
- We introduce a very early universe model based on the thermodynamics of a gas of closed strings in a background that is nonperturbative in alpha '. Upon considering the fully alpha '-corrected equations extended to include certain anisotropic cosmological backgrounds, we describe the evolution of the system in three different stages parametrized by the gas's equation of state. Using standard string thermodynamical arguments, we start with an isotropic ten-dimensional universe inside the string scale and evolve it toward a universe with four large spacetime dimensions and six stabilized internal dimensions in the Einstein frame.
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| 3. |
- Quintin, Jerome, et al.
(författare)
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Cosmology at the top of the alpha ' tower
- 2021
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Ingår i: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; :7
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Tidskriftsartikel (refereegranskat)abstract
- The cosmology of the fully alpha ' -corrected duality-invariant action for the Neveu-Schwarz sector of string theory is revisited, with special emphasis on its coupling to matter sources. The role of the duality covariant pressure and dilatonic charge of the matter sector is explored in various contexts, from the low-curvature regime to non-perturbative solutions in alpha '. We comment on how an infinite tower of alpha ' corrections allows for fixed-dilaton de Sitter solutions, even in vacuum. We further investigate the necessary conditions for accelerated expansion in the Einstein frame, as well as for non-singular bounces that could resolve the big bang singularity. In particular, explicit examples are constructed, which show that the tower of alpha ' corrections may support an Einstein-frame non-singular cosmological bouncing background, even when the matter sector respects the null energy condition.
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